Manufacture of sulphuric anhydride



Nov. 6, 1923.

'M. F. CHASE ET AL D)IA !IUFACTURE OF SULPHURIC ANHYDRIDE Filed Sept. 24, 1918 WITNESSES:

g El 0mins Be/f fag/ha AbsorpliO/r Apparatus C'anzlers/bn 4 Blower Ff/farm lp aam as flustca/cer Burner INVENTORS ATTORNEY Patented Nov. 6, 1923. I

UNITED STATES MARCH F. CHASE, OF WASHINGTON, DIS'JPIRIC'J. OF COLUMBIA, AND FBE'DEBIC E. PIERCE AND JOHN SKOGMABK, OF NEW YORK, N. Y., ASSIGNOBS TO THE COS PROCESS COMPANY, INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MANUFACTURE OF SULPHURIC ANHYDBIDE.

Application filed September 24, 1918. Serial 1W0. 255,418.

To all whom it may concern:

Be it known that we, MARCH F. Crmsn and Fnrnnuro E. PIERCE, both citizens of the United States, residing, respectively, said CHASE at Washington, D. C., and said PIERCE at New York city, N. Y., and JOHN' SKOGMARK, a subj ect'of the King of Sweden,

residing at New York city, N. Y., have in-' vented the following described Improvements in Manufacture of Sulphuric Anhydride.

The invention is an improvement in the so called contact method of making sulphuric anhydrid or sulphuric acid whereby simpler and less expensive equipment 1s required for a given production capaclty, whereby an inexpensive catalyzer may be used with high efficiency, and whereby only inert and harmless waste products need be discharged into the atmosphere, and whereby various other benefits and advan tages are obtained, as will hereafter be made apparent to those skilled 1n thls art. The invention consists in producing a gaseous medium or mixture containing sulphur dioxid and oxygen, as the elements to be combined to form sulphuric 'anhydrid, together with other gases inert in character and maintaining said mixture of substantially constant proportions while circulating it into repeated contact with the catalyzer and removing the product of the catalytic conversion, as hereinafter more fully described. The invention resides in the general and specific combination of steps and sub-combinations thereof I whereby all or some of the results stated are attained. The preferred relation of the successive steps of the method is schematically represented in the diagram drawing forming part hereof.

The sulphurous mixture is produced in an apparatus designated burner and which will be understood to be a receptacle or space in which sulphur-bearing materials such as brimstone, iron pyrites, zinc ores, etc., are burned in such manner that the efliuent will contain sulphur dioxid and oxygen in addition to nitrogen and small percentages of other inert gases inevitably present from 'furnace combustion on a commercial scale and to be regarded in the present case as diluents merely, the oxygen being present either as an excess remaining over from the combustion process or purposely added to the combustion products. The method is most efiiciently carried out in conjunction with the manufacture of oxygen from air in which case the oxygen source is an oxygen plant as indicated in the diagram, although other sources can be employed. Some of the oxygen from such a source is or may be admitted to the burner to assist combustion, through the pipe line 2- regulated by valve 3 and some of the oxygen, in highly compressed form, may be admitted to the efiluent from the burner at any other point, as for example at 1, just beyond the dust catcher through which the combustion products pass to the circulating system and the function of which is to remove ash and solid matter in suspension in said products. Introduction of the oxygen at this point, under regulation by valve 4, serves by expansion to cool the burner gases thus serving a doublepurpose of providing the necessary free oxygen for the medium andpreparing the medium for the filtering apparatus. The medium produced in this manner, whether by the admission of oxygen to the burner or to its products contains, as will be obvious, a. higher percentage of oxygen than if the burner reactions were efi'ected merely bythe admission of air and it is desirable that the sulphurous mixtureshall'be concentrated.

The gaseous products of the burner, freed from ash by the dust catcher and containing. the necessary content of free oxygen may also be passed through a filter when considered necessary in order to complete the elimination of suspended liquid or impalpable dust therein. This filter may be located at any convenient point in the path of the medium toward the conversion apparatus and is shown as situated immediately in front of the blower on its suction side. Said blower draws the mixture from the burner into a system of piping constituting the circuit of the system, the entrance to which is marked 5 and also keeps up a continuous circulation of the mixture through said circuit under the control of suitable valves. It may be variously located for this purpose and is to be understood as representing broadly a means of establishing and maintaining a proper flow andcirculation through the system. The circulating medium first encounters the conversion apparatus which comprises the preheater and the converter, containing the catalytic agent effecting the combination of the sulphur dioxid and the free oxygen in the formation of sulphuric anhydrid. Apparatus of this character is well known in the art and need not be described in detail. It involves the use of a catalyzer arranged therein to have a proper contact with the incoming gaseous medium and at a proper temperature, to the end of converting as large a percentage as possible of the sulphur dioxid into sulphur trioxid, or in such percentage as may be desired. It may be constituted of one or several converters and equipped with all such necessary or useful appurtenants as are common in the art.* The catalyzing agent may be platinum but as platinum is expensive, a cheaper agent such as iron oxid is preferred and is made available by the present invent-ion yielding an ultimate etliciency equal or' superior to platinum as presently explained.

From the converting apparatus, the gaseous medium now containing a pecentage of SO passes to the absorptlon apparatus. Here the S0 is removed by any appropriate method, as for example by allowing it to pass through a shower of sulphuric acid in a quartz-filled tower, or otherwise, and the remaining gas containing unconverted S0 and the original content of nitrogen and other diluents and possibly some sulphuric acid mist, passes on through the circuit. A spray catcher to remove and save the mist may be used at this point or as part of the absorption apparatus if desired. The gas then relatively dry continues through the circuit toward the entrance 5 of the system for replenishment at that point from the burner and for repassage through the converter, but while thus returning is subjected to a proportion-regulating gtreatme'nt. Either the whole .or part of this returning medium may thus be treated, the immediate purpose thereof being to eliminate such an amount of nitrogen and the other diluent gases as will equal the addition of diluents constantly entering the system with the fresh efiluent from the burner to thus offset the amount of product removed by the absorber and thereby keep the proportions of the medium constant. Such elimination may be accomplished in various ways and in various forms of apparatus and in the case where the oxygen supply in manufactured from air, the compressed nitrogen byprodnot from the oxygen plant is utilized expansively to cool and condense-to liquefaction the sulphur dioxid in the circulating medium, which liquified dioxid is thus rendered separable and is drawn off from the nitrogen still remaining gaseous and the latter in requisite amount is allowed to escape to atmosphere o otherwise used. The separated liquefied sulphur .dioxid, remaining after the elimination of the nitrogen, etc., is saved and returned to the main part of the circulating system for further catalytic treatment. In the diagram, the eliminator is shown as interposed in a by-pass 6 of the main circuit of the system, regulated by valves. The bulk of the medium returns direct to the blower and the by-pass carries only so much as will provide for the elimination of the proper amount of diluent gases suflicient to keep the proportions of the circulating mixture constant, or to keep the proportion of sulphur dioxid up to or above some definite minimum. The eliminator consists of a chamber or coil as usual through Which the by-passed portion of the gaseous medium is allowed to pass while cooled to liquefaction by-the expansion of the compressed nitrogen introduced in proper relation through the pipe 7 from the oxygen plant. Apparatus suitable for this purpose is well known to the art. The liquefied sulphur dioxid produced in the eliminator is returned direct to the main circuit, as above stated, as for example at the point 8 or it may be conducted in condensed form through pipe 9 to the circuit entrance 5 where its expansion on regasification may be utilized to such extent as may be desired in cooling the incoming burner gases, in substitution for or in conjunction with the cooling eflect of-the oxygen from the oxygen plant above described. It is advisable to keep the medium at a moderate tem' erature for many reasons. The amount of f i'ee oxygen allowed to enter the circulation, from the burner Or the oxygen supply is closely regulated in amount so that very little of it is left in the residual gases passing to the eliminator and very little of it is therefore wasted by exhaust to atmosphere.

From the foregoing it will be observed that a constant volume of gaseous medium containing sulphur dioxid, an appropriate proportion of free oxygen and a quantity of nitrogen and other diluent gases, is always maintained in circulation in a closed system and subject to conversion by repeated contact with a catalyzer as above explained, and that as the sulphur and oxygen are removedin the form of sulphur trioxid or sulphuric acid, the residual gases arealso removed in a like proportion or in any event so as to compensate for the continuous inflow of such inactive or diluent gases along with fresh sulphurous gases from the burner introduced to cause a high percentage of conversion on a Single pass of the gases is not vital to the at tainment of a high efliciency as in the case of existing contact methods, it being obvious thatthe surplus sulphur dioxid left over after a partial conversion is again and again subjected to contact and eventually entirely converted. Consequently the least expensive catalyzers are thus rendered available and with no attendant burden on the method beyond the mechanical power consumed in maintaining the circulation. At the same time some of the chemical objections to the use of platinum are eliminated. Where the oxygen plant is operated solely to supply the process as above described, a surplus of highly compressed nitrogen will be produced and we utilize the expansive force of such surplus for motive power to drive the main blower above described. For this purpose, in the diagram, the nitrogen pipe 10 runs to the blower engine 11 which 1s a variable s eed motor belted to the blower pulley.

rom the exhaust of the motor the nitrogen may be conducted to any other place of use.

It will beapparent to those skilled 1n the art that the principle of the process above described may be applied in different ways and that there is no intention to limit the same to the employment of any particular type of apparatus or to any particular sequence of steps, or to any particular manner of performing said steps, and also that various additions and subtractions may be made to the process as described without departing from the following claims: 7

1. A method of manufacturing sulphuric anhydrid which. consists in making a mixture of gases containing the elements of the product together with other gases and circulating said mixture repeatedly through apparatus adapted to combine the said elements and produce the product and through apparatus adapted to remove the same from' the mixture, replenishing said circulation with fresh mixture and eliminating some of the said other gases to maintain proportions in the circulating mixture.

2. The process of manufacturing sulphuric anhydrid which consists in circulating a mixture containing sulphur dioxid, oxygen and diluent gases in substantially constant proportions into repeated contact with a cataly'zer while removing the product of the catalytic conversion.

3. A process of manufacturing sulphuric anhydrid, etc., which consists in circulating a mixture containing sulphur dioxid, oxygen and diluent gas, subjecting the circulating mixture to catalytic conversion, absorbing the converted product and controlling the proportions of the circulating mixture to sion.

4; The process specified in claim 3 wherein the elimination of a portion of the diluent gas is accomplished by cooling the mixture to the point of liquefaction of the sulphur dioxid therein and separating and returning the latter to the system without the unliquefied portion of the cooledmixture.

5. The process specified in claim 4 characterized also by the return of the liquefied sulphur dioxid to the system at a point where its expansion may cool fresh mixture entering the system.

6. The ste in the manufacture of sulphuric anhy 'd, etc., which comprises admitting oxygen (as distinguished from air) to a suitable burner and burning sulphurbearing materials in said burner to produce a burner efiiuent containing a relatively highpercent of sulphur-dioxid, ad oxygen to sai effluent, and subjecting suc mixture to catalytic conversion.

7 The process of manufacturing sulphuric anhydrid, etc., which consists in burning a sulphur-bearing material, in a I suitable burner, asisting the combustion by admitting oxygen (as distinguished from air) theretqand thereby producing a burner eflluent containing a relatively high percentage of sulphur-dioxid, repeatedly circulating said efliuent, subjecting said circulate ing efiluent to catalytic conversion, absorbing the converted product and controlling the proportions in the circulation to maintain a predetermined rate of conversion.

8. The rocess of making sulphuric anhydrid' whlch consists in circulating a mixture containing sulphur dioxide, oxygen and diluenhgas, repeatedly, through a catalytic conversion apparatus and through absorber apparatus, and maintaining 'substantially constant proportions in .the flow through said catalytic apparatus by eliminating a part of the delivery from the absorber and replenishing the circulation with fresh mixture.

9. The process of manufacturing sulphuric anhydrid which consists in circulate ing a mixture containing sulphur dioxide,

oxygen and diluent gas, repeatedly, through catalytic conversion apparatus and through rating oxygen and nitrogen from com premed air, using the residual compressed nitrogen to eliminate a part of the diluent gas from the circulation and using said oxygen to replenish the circulating mixture.

In" testimony whereof, we have signed this I an absorber of the converted product, sepa- 

